In the fields of medicine, veterinary, and pre-clinical or laboratory research the need to insert penetrating members (such as needles and lancets) into living tissues is ubiquitous. Some of the reasons necessitating tissue penetration and insertion of penetrating members include: to inject medications and vaccines, to obtain samples of bodily fluids such as blood, to acquire a tissue sample such as for biopsy, or to provide short or long term access to the vascular system such as intravenous (IV) catheter placement.
Of the 39 million patients hospitalized in the United States, 31 million (80%) receive an IV catheter for nutrition, medication, and fluids. Obtaining peripheral venous access is complicated by loose tissue, scar tissue from repeat sticks, hypotension, hypovolemic shock, and/or dehydration. These factors manifest in easily collapsed veins, rolling veins, scarred veins, and fragile veins making venipuncture problematic. Most hospitals allow a clinician to make several attempts at peripheral IV access before the hospital “IV team” is called. Studies have shown that success can improve significantly with experience. There are also a number of techniques that can be used such as tourniquets, nitroglycerin ointment, hand/arm warming, but these require additional time, are cumbersome, and do not work effectively in all situations. Tools are also available to improve visualization of the vasculature that use illumination, infrared imaging, or ultrasound. These tools, however, do not simplify peripheral venous access into a collapsible vein. In emergency situations, a clinician will often insert a central venous catheter (CVC) or possibly an intraosseous line. These procedures are more invasive, costly, and higher risk. Multiple needle sticks significantly increase patient anxiety and pain, leading to decreased patient cooperation, vasoconstriction, and greater opportunity for infection and complications. Repeated attempts to obtain venous access are costly to the healthcare facility; estimated at over $200,000 annually for a small hospital. In endoscopy facilities, which see large numbers of older patients, the problem is further exacerbated by fasting requirements that decreases the pressure in the veins. During cannulation, the needle and catheter push the near wall of the vein into the far wall, collapsing the vein—inhibiting the ability to place the needle into the inner lumen of the vein.
Tissue deformation during needle insertion is also an issue for soft tissue biopsy of tumors or lesions. Conventional needles tend to deform the tissue during the insertion, which can cause misalignment of the needle path and the target area to be sampled. The amount of tissue deformation can be partially reduced by increasing the needle insertion velocity, and so this property has been exploited by biopsy guns on the market today.
Blood sampling is one of the more common procedures in biomedical research involving laboratory animals, such as mice and rats. A number of techniques and routes for obtaining blood samples exist. Some routes require/recommend anesthesia (such as jugular or retro-orbital), while others do not (such as tail vein/artery, saphenous vein or submandibular vein). All techniques utilize a sharp (lancet, hypodermic needle, or pointed scalpel) that is manually forced into the tissue to produce a puncture that bleeds. A capillary tube is positioned over the puncture site to collect the blood droplets for analysis, or the blood may be collected into a syringe or vacuum vial. Regardless of the sharp used, if an individual is properly trained the procedure can be performed quickly to minimize pain and stress. It is important to minimize stress as this can interfere with blood chemistry analysis, particularly for stress-related hormones. Another much more expensive strategy is to place an indwelling catheter and obtain blood samples in an automated device. However, the catheter cannot be left in over the life span. In addition, the tethering jackets and cables, which must remain in contact with the animal, will likely cause stress. Microneedles can be implanted with highly reduced insertion force and less pain, but may not produce a large enough puncture to yield significant blood for collection and analysis.
Research supports that needle vibration, or oscillation, causes a reduction in needle insertion forces. The increased needle velocity from oscillation results in decreased tissue deformation, energy absorbed, penetration force, and tissue damage. These effects are partly due to the viscoelastic properties of the biological tissue and can be understood through a modified non-linear Kelvin model that captures the force-deformation response of soft tissue. Since internal tissue deformation for viscoelastic bodies is dependent on velocity, increasing the needle insertion speed results in less tissue deformation. The reduced tissue deformation prior to crack extension increases the rate at which energy is released from the crack, and ultimately reduces the force of rupture. The reduction in force and tissue deformation from the increased rate of needle insertion is especially significant in tissues with high water content such as soft tissue. In addition to reducing the forces associated with cutting into tissue, research has also shown that needle oscillation during insertion reduces the frictional forces between the needle and surrounding tissues.
Recently, a number of vibration devices have been marketed that make use of the Gate's Control Theory of Pain. The basic idea is that the neural processing, and therefore perception of pain, can be minimized or eliminated by competing tactile sensations near the area of pain (or potential pain) originates. Vibrational devices may be placed on the skin in attempt to provide “vibrational anesthesia” to an area prior to, or possibly during, a needle insertion event. Research has shown that tissue penetration with lower insertion forces results in reduced pain. The Gate Control Theory of Pain provides theoretical support for the anesthetic effect of vibration. The needle vibration may stimulate non-nociceptive Aβ fibers and inhibit perception of pain and alleviate the sensation of pain at the spinal cord level. In nature, a mosquito vibrates it's proboscis at a frequency of 17-400 Hz to reduce pain and improve tissue penetration.
Other vibrating devices directly attach to a needle-carrying syringe and employ non-directional vibration of the needle during insertion. Reports suggest that this type of approach can ease the pain of needle insertion for administering local anesthetic during dental procedures, and to enhance the treatment of patients undergoing sclerotherapy. These non-directed vibration techniques do not allow for precise direct control of the needle tip displacements, and by their nature induce vibrations out of the plane of insertion, which could increase the risk for tissue damage during insertion. Furthermore, existing vibrational devices for improving needle insertion cannot be readily integrated into a control system which would allow for the ability to control and/or maintain the magnitude of needle oscillation during insertion through a wide range of tissue types.
A need exists to improve the insertion of penetrating members (such as needles or lancets), by reducing the force required to insert them, causing less tissue deformation, and inducing less pain and stress to the patient, research subject, and clinician/researcher. As such, there remains room for variation and improvement within the art.